1. Field of the Invention
This invention relates to a high density magnetic recording medium and more particularly, to a magnetic recording medium adapted to be used for tapes for digital VTR or HD-VTR as well as for a large capacity floppy disk or the like.
2. Description of the Prior Art
Magnetic recording of information on a magnetic recording medium is generally effected by using the magnetization of magnetic particles in the longitudinal direction of the magnetic recording medium. With such method shown above, however, it is difficult to improve the recording density as to exceed a limited level because high densification of recording may result in an increase in the demagnetization of the recording medium.
Under such circumstances in order to exceed such a limited level on the recording density, a perpendicular magnetic recording method has been proposed recently, which uses the magnetization of magnetic particles in the perpendicular direction to the surface of the recording medium (see, for example, Shunichi Iwasaki; "High Density Magnetic Recording Using Perpendicular Magnetization", Nikkei Electronics, Aug. 7, 1978, pp 100-111). The above-mentioned perpendicular magnetic recording method features that the demagnetization in a recording medium is decreased in the high density recording range, so that it can be said to be a method substantially adapted to be used for high density recording.
As the recording medium used for the perpendicular magnetic recording method, there may be a continuous film such as Co-Cr evaporation film or the like and a coated film having plate-like hexagonal barium ferrite particles or the like dispersed in a resin (see, for example, Japanese Patent Application Laid-Open Nos. 60-149105 and 1-251420). Particularly, the coated film type of perpendicular magnetic recording medium has been watched with a keen interest from the practical viewpoints of, for example, the cost-effectiveness and durability (see, for example, O. Kubo, T. Ido and H. Yokoyama, IEEE Trans. Magn., MAG-18(6), P 1122 (1982)). With the coated film type of perpendicular magnetic recording medium, plate-like magnetic particles to be dispersed each has the easy-axis of magnetization in the perpendicular direction to the plate surface thereof. As a result, plate-like magnetic particles whose easy-axis of magnetization is easy to orient in the perpendicular direction to the supporting base body in coating process are employed. However, even if an easy-to-orient magnetic powder is used, suitable orientation can not be attained only by coating them on a base film using a general method, which means that it is difficult to obtain a perfect perpendicular magnetic recording medium. On the other hand, barium ferrite magnetic particles are extremely fine and plate-like in shape with a thickness of 100 to 1,000 angstroms, which means that these particles may be advantageously used as a longitudinal orientation medium.
In order to improve the recording characteristics of a magnetic recording medium in the short wave-length range, many attempts have been made to make the surface roughness thereof small in the allowable practical property range as well so as to make the residual magnetization of the recording medium large.
With hexagonal ferrite magnetic particles such as the above-mentioned barium ferrite, however, it is well-known that their saturation magnetization is small, which means that a limitation will be naturally imposed upon the improvement of their magnetization value. As a result, in order to improve the magnetization of a magnetic recording medium, an attempt has been made to use finer magnetic particles to increase the packing density, or the magnetic particles per unit volume, has been made as one of means for this purpose. In this case, however, an increase in packing density makes it possible to improve the magnetization thereof up to a certain level of range, but results in the deterioration of the surface roughness of the recording medium. Furthermore, extremely fine magnetic particles results in decreasing the dispersivity of magnetic particles in a magnetic paint. There arise problems as above to be overcome. In addition, as the hexagonal ferrite powder to be used for the magnetic recording application, that with Co-Ti substitution is generally well-known, which results in an increase in coercivity distribution, so that when it is used as a recording medium, the transition length of recording becomes large, which is disadvantageous.
As described above, a conventional magnetic recording medium has had a limitation upon the improvement of its output property in the high density recording range.